This invention relates generally to the protection of plants from pathogen attack, and particularly to protection from Oomycete pathogens.
One of the largest problems facing agriculture today is effective control of plant pathogens. Compounds that are biologically derived and toxic only to specific target organisms are preferred for control of plant pathogens, because of their decreased impact on the environment and on non-target organisms.
Plants, especially those growing in freshwater environments, must have disease resistance mechanisms to cope with aquatic plant pathogenic organisms that may invade and destroy them. Oomycetes would be expected to attack plants that normally exist in strictly aquatic environments. However, aquatic plants seem to thrive and be relatively disease free in these ecosystems. This biological conundrum may be related to extrinsic factors controlling plant disease resistance. Epiphytic or endophytic microbes may associate with aquatic plants and produce antioomycetous compounds. If such compounds exist, they may prove agriculturally applicable to plant disease control situations in which Oomycetes are a problem.
Metalaxyl is well established as the agent to which the Oomyctes are the most sensitive. However, increasing resistance to metalaxyl is developing in certain Oomycete populations and this agent is being rendered increasingly less effective. Lyr, H., Modern Selective Fungicides (Gustav Fischer Verlag: New York, Jena., 1995). Thus, a need exists for new compounds to combat these plant pathogens.
The invention provides oocydin A, a mono-chlorinated lipophilic macrocyclic lactone possessing selective antioomycetous activity against Oomycete plant pathogens.
The invention also provides Serratia marcescens MSU-97, an isolate that produces oocydin A into culture medium. The invention thus provides a method of making and purifying oocydin A.
The invention further provides an environmentally desirable method of controlling and preventing Oomycete infestation of plants by administering the compounds of the invention to plants.